Carbonyl process



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ATTORNEY ro vAcuu/u PUMP 74 THROUGH VALVE srsrEM Patented Oct. 5, 1954 .CARBONYL PRGCE S S .lames J. Lander, Watchung, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York ApplicationJanuary A18, 1950, Serial No. 139,301, which is a continuation of application Serial No. 660,140, April 6,1946. Divided and this .ap- ,plication March 14, 1951, 'Serial No. 215,522

(Cl. V117-50) 3 Claims. l

This invention relates to processes Afor coating metals such as iron, steel, nickel, copper or other metals and ceramics or vitreous materials, or any other materials capable of withstanding suiciently high temperatures to be plated with metals or carbides of chromium, tungsten, or molybdenum or compositions including a plurality oi such metals or their carbides or mixtures vof one or more of such metals or one or .more of their carbides.

This application is a division `of my application Serial No. 139,301, led January v18, '1950, which issued as Patent No. 2,602,033 on July 1,

'1952, which is a continuation of my application Serial No. 660,140, filed April 6, 1946 which Was abandoned March 7, 1950y which `in turn is in part a continuation of my applications Serial N0. 504,418, iiled September 30, 1943, which issued as Patent No. 2,516,058 on July 18, 1950 and -Serial No. 525,123, led March 4, 1944 and abandoned February 19, 1949, and all rights, priorities, vand benefits arising from such facts are claimed.

Others have previously Suggested Vthe vplating of metals with certain other'metalsdeposited-from metallic carbonyls under conditions alleged to deposit pure -or adhering layers but such suggestions have been deiective 'and insuicient 'in setting forth `the conditions necessary to deposit pure metals or adherent layers and also have failed to recognize that carbides maybe so deposited.

There will herein be set forth conditions which must be observed and features of operation and procedure necessary to effect substantial improvements not disclosed by prior Workers inthe art.

, The metals, tungstein,molybdenum or chromium, may apparently exist in diferentcrystalline forms and they also may form several carbides. In accordance with features of the present invention, the processes described maybe controlledto `crystalline structure and a cubic crystalline struci ture. Conditions may ybe-controlled so that one or the other of these forms of-the material may be deposited in the plating.

For certain purposes it may be desiredtorplate -or -cover the surfaces of metals or similar -objects with coatings, especially tightly Aadhering kcoatings of one or .another -of such carbides or mixed carbides of these metals, or of :the metals themselves. 'For example, anelectric'al contact ject.

'consisting essentially of W2C to make it a lgood emitter of electrons when heated or M020 or 'W2C may be plated to form a hard facing on the ob- Among such objects to be plated within the scope of the invention are .included space discharge filaments, grids, anodes, electrical contacts, metal cutting tools having their VWorking 'faces plated, metal Working rolls having .their working faces plated, metals to be subjected vto corrosive gases at high pressures or high temperatures, or both, either-or not coincident with mechanical impact, wire drawing dies, bearings, such as clock, watch or compassbearings, mirrors for any purpose such as reectors of .atronomical telescopic instruments.

A feature of the invention relates tothe stabilizing effect of carbon monoxide under different conditions of temperature and pressure'upon control of the production of delnitecarbides or relative portions of metals and carbides.

Another feature relates to the avoidance of the detrimental-eifect of impurities.

Another feature relates to preventing the exist.- ence of conditions inhibiting the formation of pure metals or conditions inhibiting the formation of carbides in general, or conditions inhibiting the production of particular carbides and promoting the production and deposition of the particular metal carbide-or alloy which is to be deposited.

The invention may be applied lto the plating of objects which have internal surfaces, undercut surfaces, depressions or grooves or irregular surfaces with simple or mixed metals, carbides or alloys of the class mentioned, a matter of irnportance because it is often difficult to deposit material uniformly by plating upon internal surfaces, recesses, or in the bottoms of grooves of objects.

A feature of the disclosure relates to the removal of foreign bodies such as metallic oxides .from the surface to be plated to such an extent that foreign bodies of natures and in such'small quantities as one might think inconsequential are removed.

Other features of the invention relate to methods of promoting adherence of theplated metals, alloys or carbides to the surfaces to beplated, to the effects of varying one or more of the nature,

3 pressure, temperature, purity, and kind of gas content supplied to the plating tank chamber, methods of and apparatus for causing plating to be applied on desired surfaces only, and control of the crystal structure or atomic arrangement of the applied plating by controlling pressure, temperature and influx of gases supplied coadjuvantly with the gas or vapor.

A special feature of the invention relates to the use of a continuously maintained reduced pressure in the plating chamber. It is accomplished by sufficiently slow introduction of the metallic carbonyl and other gases coincident with a sufficiently rapid and powerful pumping maintained at a very low degree of pressure in the plating chamber. It is believed that this gives the molecules of metallic carbonyl a long, mean free path whereby the effects of thermal dissociation may be controlled and pure and more ad herent coating produced.

Another feature of the invention relates to the control and rate of deposition by introducingcarbon monoxide or hydrogen or one of the other or both of these gases in controlled proportions to control the plated composition.

Another feature of the invention relates to the introduction also with the hydrogen of a limited and properly controlled amount of water vapor which, in the case of plating molybdenum or tungsten on certain kinds of objects, is found to be beneficial. In plating with chromium the use of water vapor is excluded and, furthermore, in plating base metals or materials containing substantial chromium contents the use of water vapor is excluded. Thus, for example, in plating molybdenum or tungsten or their carbides upon a kind of steel known as Stellite which, in a typical form includes about 27.5 per cent chromium, the use of water vapor is excluded because the chromium becomes oxidized and results in a poorly adherent plate. However, in plating such objects with molybdenum or tungsten the plating may be initiated and carried through the preliminary stages with the exclusion of water vapor and thereafter water vapor may be introduced either for the purpose of controlling or varying the plated composition or for other reasons. In this case the initial deposit of molybdenum or tungsten or their carbides forms a protective layer over the Stellite or other material, which cannot be exposed to heated water vapor in the plating chamber, so that thereafter the water vapor may be introduced.

Carbonyls of tungsten, molybdenum and chro mium are white solids which decompose at temperatures of around 150 C. and they have substantial vapor pressures ranging from l5 to 60 millimeters of mercury at 100o C. When they decompose upon a hot metal or similar surface under properly controlled conditions a film of metal or carbide of the metal of the carbonyl or carbonyls is deposited upon the hot surface.

A difficulty encountered in securing adherent deposits has been found to be due, in part at least, to foreign substances upon the surface. Cnc of the most troublesome foreign substances u pon the metal surfaces are undesired metal oxides.

A surface to be plated which is suitably free from oxides and other substances may be and has been produced by abrasion, electro-etching, or other chemical methods with preventie-n of subsequent contamination. Speeifically, the metal object to be plated may be treated with acid and washed free of adherent acid in an organic solvent suoli as alcohol and thereafter placed in the plat- 4 ing vessel hereinafter referred to and subjected to immediately applied vacuum. This serves to remove the residual alcohol by evaporation.

The object to be plated may be treated preliminarily to the introduction of the carbonyl gas by heatingl to relatively high temperatures such as 600 C. in a vacuum which is maintained by operating the vacuum pump. This tends to clean the surface.

The object to be plated may thereafter be raised to the desired plating temperature, the carbonyl vapor admitted, and the plating accomplished.

However, hydrogen may be admitted to the plating vessel prior to the plating operation with the result that the surface to be plated may further or more effectively cleaned, with the result of a more perfectly adhering plate. Hydrogen may be admitted to the plating vessel either immediately or after the object has been subjected to vacuum or heat or both for a period of time. The hydrogen is admitted from a suitable inlet and removed by a vacuum pump through suitable outlet and during the time the object to be plated is exposed to the hydrogen the temperature of the object to be plated may be raised as high as 600 C., more or less, dependent upon the nature of the object and its surface impurities with the result that oxides and other substances upon the surface are more thoroughly removed. Thus, for example, oxides will be reduced and the oxygen will combine with hydrogen to form water and carbides lose their carbon and the carbon thereof is combined with the hydrogen to form hydrocarbons such as CH4. These hydrocarbons are carried out with the hydrogen and eliminated.

The admission of some hydrogen during the plating operation along with the carbonyl vapor and the carbon monoxide gas may be through either the same inlet which supplies the carbonyl vapor or through a separate inlet. in either case an effect of the hydrogen is to produce an effect analogous to that which in electrolytic plating is sometimes styled throwing power which signifies that plating in crevices, grooves or depressions is more effectively accomplished and the metal plate is applied more uniformly over the surface to be plated.. The influx of hydrogen for the purpose of plating with carbides is subject to the limitations hereinafter set forth.

The deposition of adherent carbide coatings may be accomplished at relatively low temperatur-es and moderately low vacua with little or no influx of carbon monoxide gas, as increasingly better vacua are employed the use of proportionately greater amounts of carbon monoxide is desirable. The nature of the carbide deposit is also variable with conditions, thus with little or no carbon monoxide gas, at pressures of a few millimeters of mercury, and at low temperatures molybdenum and tungsten carbonyls form chiefly face-centered M020 or W2C, whereas with higher pressures, higher temperatures, and greater CO gas concentration, in the case of molybdenum carbonyl, MOC is formed. One may introduce appreciable quantities of hydrocarbons of low molecular weight such as methane Cl-Il into the plating vessel in the case of plating carbides, especially after the bond has been formed.

Under certain circumstances plating may be accomplished by the use of metallic carbonyl vapor alone in a pure form. For example, in order to plate an iron surface the plating may be started at a sufficiently .high temperature to secure satisfactory bond of adherence and deposit metal from molybdenum, tungsten or chromium carbonyl gas. In plating molybdenum, for-example, at a relatively high plating temperature beginning-at about 600 C. and continuing in the range of 400 C. to `5005C., metallic molybdenum is deposited 4provided the iniiux of -carbonyl gas is maintained sufciently low and the Vacuum is maintained also sufficiently low `to l'hold the carbon monoxide gas, ACO, to a low concentration. AVAt'a lower plating temperature, for example, 200 "C. to 400 C., a carbide plating is deposited which has a face-centered cubic arrangement. The tendency is to deposit the Vcubic carbide at low temperatures and at high concentrations of carbon monoxide. As the temperature is raised and as the -concentration of carbon monoxide is lowered, the tendency is to deposit the pure metal molybdenum. At a high temperature and at a relatively high carbon monoxidepressure, the tendency is to deposit a carbide molybdenum M020 which is hexagonal in form. Similar tendencies are noticeable in the-case of plating from tungsten carbonyl vapor except that no plating occurs in the Arange around 200 C. to 300 C. and so far as has been determinable from X-ray analyses, the hexagonal carbide WzC has not been produced. However, a fcubic carbide of tungsten may be produced. The Yboundary zone between pure metals and carbides Vis the combined function of temperature 'and carbon monoxide pressure. The pressures used may range from about 1/1000 to 10 or 12 millimeters of mercury. llrom X-ray analyses supplemented by chemical analyses `the coatings or platings described as cubic molybdenum carbide occur roughly with the empirical formula MozC although the carbon content in atomic percent varies over a range from around 25 atomic per cent up to about 35 atomic per cent.

Plating vmay also be accomplished by introducing puried hydrogen -along with the gaseous carbonyl in amounts ranging from moderate to very considerable, for example, up to Y-1000 moleculesof hydrogen per molecule of -carbonyl Vapor. Heating the surface to be plated in hydrogen is beneficial in reducing surface oxides, and, in some cases, it Vimproves the bond `between the .plating and the surface to be plate'd'and, in other cases, it appears to be Vfairly 'essential to producing a vsatisfactory bond. When the ratio `of rhydrogen to carbon monoxide gas in the plating f 'chamber becomes large, the'tendency is to remove carbon so -that pure metals vmay be plated `at 'somewhat lower 'temperatures and `higher pressures. In general, in plating chromium thereis a greater tendency to deposit both oxides land carbides than in the case of molybdenum and 'tungsten and in the case of this 'metal and lvextremely pure metal free -from *carbides -is not deposited but the plating may be made extremely hard. It appears that metalic tungsten can be "plated at considerably higher pressures than 4in the case of molybdenum and therefore :the "plating rate in the case of tungsten may be higher.

Under many circumstances platings or .coat- -ings containing Aconsiderable'carbon are more v-metals -as `nickel, `iron, -copper and numerous i 6. forms of fst'eel. 'Somefsteels such as those v'containing chromium, will vbe oxidized by water vapor-and, consequently, :water vapor or so-called wet hydrogen may not be usedin plating them, although v'the plating may -be started without water vapor and after a suicient layer to protect `the plated object lfrom the water is deposited, the water vvapor may '-be introduced and the plating continued. Subject to "these limitations wet hydrogen may be utilized and is 'benecial when it may Abe desired to 4prevent l'the deposition of carbon inthe plating. 'For example, in plating molybdenum `at 625o C. Ain a plating 'gas containing 2 4molar per centof water, plating was `found by analysis Ito contain 0.1'5 atomic p'er cent of carbon with a slow plating rate. `-However, with a-considerable faster platin'g'rate and by using f8' molar per-cent of water, the plating contained 1.8 atomic per cent of carbon and vwith a still higher plating rate and 25 molar per cent of water, the plating contained '7.0 atomic percent of carbon. Therefore, while water vapor is useful in reducing 'the carbon content, the carbon content can be `kept extremely low only at a relatively low vplating rate although `these may lbe somewhat 'higher than may `be used for depositing a similar composition without the use of water.

However, one should not conclude that the introductionof oxygen from lthe air is equivalent to 'a small added amount of water vbecause the experimental vevidence is tothe contrary andthe introduction of an amount of air equivalent to one per cent oxygen has been found to result in va -very inferior plating.

As stated above the introduction Lof water re- 'sults in a -Softer plating, thus, :in plating `molyb- 'denum at 500 C. and at certain conditions with no 4water the Vickers -hardness o'f the plating -was 1030; with two per cent `water 1000; and with eight per cent water it was 800. In plating at 550 C. under similar conditions with no water the hardness was 920; with two per -cent water the hardness was 740; with eight per cent water the hardness was 430. Brittleness is 'a 'factor and for certain purposes, 'such as producing -a Wearresistant-coating on dies, rolls, or machine tools, 'hardness is highly desirable, but extreme brittleness -is not desirable. For Vsuch purposes it appears that the best type of plating will be one containing considerable carbon but no carbide as `such'because the presence of the carbide makes the coating more brittle without increase Aof hardness. Similar considerations apply Vto the production `of tungsten plating. For example, platings of tungstencontaining considerable carbon plated at 450 C. to 500C. in dry hydrogenat a rather high pressure ymay have va hardness measured on the Vickers scale vabove 2000. In plating chromium only relatively hard coatings ranging from'Vi'ckers 1200 to 1600 have been produced.

As previously stated, preliminary cleaning Iof a metallic specimen by abrasionin absolute alchol isa satisfactory'method of producing a l.surface to be plated. Also in plating some alloys such 'as Stellite electrochemical polishing can "be employed. A preliminary step of introducing hydrogen vbefore the metallic carbonyl rvapor is v'introduced is often ybeneiicial in iproducing a "surface 'to which the plating will -orm -a good bond. At temperatures of 500 VC. to 800 C. Vwet Ioyed steel surfaces can under conditions of high purity of hydrogen and good preliminary abrasion be satisfactorily cleaned at 500 C. in hydrogen containing from two to eight per cent water vapor, a more satisfactory technique is to use only dry hydrogen until the temperature of the specimen rises above 500 C. whereupon the wet hydrogen is introduced and the temperature rises continually to 800 C. In plating copper wet hydrogen has been found to be satisfactory in heating the specimen from room temperature to 800 C. In the case of Stellite all Water must be vigorously excluded and a very high temperature is required for adequate cleaning. Temperatures up to 1000 C. up to 1100Q C. have been used. As a general rule, bonding of the plating to the metal to be plated is more satisfactory if the plating is started at relatively high temperatures. Thus in the case of copper a temperature of around 800 C. is suitable and appears to be beneficial. As previously set forth, a high plating rate is undesirable during the bonding step as colloidal particles consisting largely of carbide tend to be produced. Consequently, good bonds require a low plating rate and, in practice, it often been found desirable to use a rate one-tenth of that which is used at a later stage of the process.

Substances other than metals may be plated within the limits that the substances must be such as can withstand the required high temperature. Within this limitation glass, vitreous materials and other materials may be plated, it being understood, however, that the considerations for forming a good bond vary with the substance which is to be plated.

Foreign materials such as water, air and organic materials must be guarded against whether present in the carbonyl or whether arising from supports or other elements in the plating chamber or whether introduced through leaks in the evacuated system or from other causes. The introduction of such substances is likely to lead to unsatisfactory or, at best, to unpredictable results.

The process may be employed for the formation of plates consisting of alloys. Thus, for example, an alloy of molybdenum and tungsten may be deposited by utilizing carbonyls in a molecular ratio approximately equal to their vapor pressures. Specimens plated at 600 C. with wet hydrogen and at a moderate plating rate were quite hard and brittle while molybdenum alone plated under similar conditions is soft. By employing separate carbonyl chambers with separate controls alloys of various compositions may be similarly produced.

Apparatus useful or convenient for plating the various bodies is illustrated in the accompanying drawings where:

Fig. l is a diagram of essential parts of an apparatus which may be employed for plating objects such as sheets, plates, bars, contacts, electrodes, etc.;

`Fig. lA is a modification of a fragmentary part of Fig. l between the section lines X-X and Y-Y modified to illustrate one method of securing a suitably thick layer of plating upon the inner surface of an orice of a metal body;

Fig. 1B is a further modification of a fragmentary part of Fig. l taken between section lines X-X and Y-Y illustrating a method which may be employed for plating portions of metallic objects and in plating other portions thereof to an appreciable extent;

Fig. 2 illustrates the modified method of mounting a relay armature so as to plate the working surfaces of its contacts;

Fig. 3 illustrates a method of mounting metallic discs upon a vitreous body to prevent one surface thereof from being plated appreciably while causing other surfaces to be plated;

Fig. 4 illustrates apparatus suitable for plating one side of a disc or sheet of material illustrated as a vitreous material but which may be metal or other substances;

Fig. 5 is a diagrammatic illustration, partially in cross section of an arrangement employing a moving injector for uniformly plating the interior surface of a body-having a cylindrical or approximately cylindrical opening therethrough; and

Figs. 6, 7, 8 and 9 illustrate details of the apparatus of Fig. 5.

Referring to Fig. l and its operation, a ceramic or glass vessel i0 is provided w' h a cooling water jacket II having a water inlet i2 from a suitable source of supply and a water outlet I3. The inlet and outlet may be located on any suitable portions of the glass or ceramic vessel. The vessel I0 which is illustrated as tubular in form is provided with a large tightly fitting stopper I4 which may be made gas-tight by means of ground glass surfaces or otherwise and has connected to it two other tubes i5 and I6 which are U-shaped. Tube I5 is provided with valves i1 and I'Ia and a side inlet tube I'ib with a valve I'Ic. Tube I6 is provided with a valve I8. A winding or coil 23 adapted to be traversed by high frequency current supplied from a suitable high frequency source it is hung, mounted or otherwise disposed about the tube I0.

An object 20 of metal to be plated or a group of objects may be placed inside the tube I0 by removing the stopper It; the specimen 20 may be placed on wedge-shaped supports 2I of glass, mica or ceramic material or otherwise hung, supported or disposed within the vessel i0. in some instances it may be merely suiiicient to lay the object 20 or group of objects within the vessel I0. The object 20 or objects 20 may consist of iron, nickel, any type of steel or ferrous, cobaltous or nickelous alloy known to the art, as well as metals or alloys of the metals tungsten, vanadium, titanium, molybdenum, tentalum, copper or stainless steel, tool steel, gun metal, cutlery steel, brass, bronze or any other metal of properties similar to these. It may consist of a metallic object to be plated or coated for artistic reasons, or durability, or to produce a hard surface resistant to abrasion or a surface resistance to chemicals in gaseous or liquid form and may be of any shape which may be heated sufficiently uniformly upon the surface or surfaces to be plated by means of high frequency induction. Carbonyl powder, for example chromium, tungsten or molybdenum carbonyl powder is placed in one of the U-shaped tubes, for

example, tube I5, and the tube is maintained cold by being immersed in brine, ice water, solid CO2 or other suitable medium in a container 24. If valves I'I and Ila are closed, the tube i5 need not be cooled. rIhe tube I6 is connected to a vacuum pump and the valve I8 opened to thoroughly exhaust the vessel I0 of air.

An alternative object 20a, consists of a grid fOr a vacuum or space discharge tube which has a stem 2Gb by which it may be mounted in the tube for use; for plating the stein 2Gb is mounted in an opening a block 2:!a ot porcelain orglass from this diagran-nnatio,r indication one is not to infer thatgrids 20a and blocks 20: would be plated at, one time or that the high frequency heating field suitable for a block 2i) would be suitable for a grid 20a; in practice a number of grids might be mounted in a multiple block 2Ia and plated at one operation. The gridsv could be oi nat mesh, cylindrical mesh or other desired shape and spacially positioned in the heating iield as cle- Sired or as necessitated by their respective conformations.

As a preliminary operation, after inserting the object. 20 and closing the vessel l0, the carbonyl may be purified by placing; it in,4 either tube l5 or lr6, exhausting the vessel lo', warming the tube in which the carbonyl is placed, chilling the other tube with solid CO2 mixture and passingy in pure hydrogen, over the carbonyl to distill the metallic carbonyl from one tube to the other; gaseous impurities such as H2O vapor may thus be reduced or eliminated with the hydrogen. This operation may be repeated one or more times or itsequivalent may be performed in a separate vessel before placing the carbonyl powder in the apparatus illustrated. The advantage of doing it in the same apparatus lies in the certainty with which recontamination of the material is prevented. We mayy assume that this step has been performed, if necessary and the carbonyl is in the tube I6 at the beginning of the plating operation.

After the exhaustion or during the exhaustion of the vessel l hydrogen may be admitted through tube l or I6, preferably in a slow stream through tube l5 until substantially the entire gas content of the tube consists of hydrogen whereupon the switch 22 is closed and the specimen heated to redness by high frequency induction with energy supplied from the coil 23. The hydrogen isv then thoroughly exhausted by continuing the operation ofV the vacuum pump with the valves lla, I'Ib, and llc; tightly closed. This tends to remove final traces of impurities. During all this time the carbonyl powder in tube l5 is kept coOlby the ice Water bath. The specimen 20 is now allowed to cool to a suitable platingtemperature, forl example around 450 C. The plating temperature may approach 150 C; and the upper limit may apparently approach near the melting point of the metal to be plated. The specimen has been cleaned and all oxides, or substantially all oxides, grease, lm, etc. have been removed from its surface by the heating to redness inthe presence of hydrogen gas. The vessel 2li is 110W replacedwith another vessel containing warm water at a temperatureof about 20 C; and the Water in the Water jacketv l l is meantime held at around 20 C. The operation of the vacuum pump at the outlet of tube l5 is continued and at this stage,- orbefore, if desired, a vessel 25 nlled with ice water may be. placed around the tube I6. The carbonyl powder in the tube l5 is now vaporized and. passes through the tube. l0, with. the result that there is: de.- posited upon the; surface of the specimen' 2D a coating of carbides. of ungsten, molybdenum or chromium,l as the ca sev may be, of a tlloknessV of aboutzamilsin approximately 30. minutes. Rapid deposition of. the, coating is desirable and con.- tnuous pumping at the outlet of tube it is necessary to remove the carbon monoxide which is formed. The tube |76, being immersed in ice Water or other low temperature medium', such as sol-id CO2, serves as atrapto precipitate and recover any unltoacted carbonyl. After the deposit on theobjoct 2 f0 has reached the proper dimensiones may be determined by observation or experiment, the interior of the vessel l0 may be restored to atmospheric pressure, the stopper I4 removed, and the obiect 2! becomes accessible for removal from the vessel.

a particular ease 0.32,A cubic centimeter per secondy of Ha was passed over molybdenum carbQnyl maintained at 16. C.. for 60 minutes at a plating temperature ot 370 C., to produce a plate thickness of 0.002,2. inch; which contained 25.0. atomic per cent carbon and was estimated to consist of per cen-t molybdenum, or- MozzC, in emma. or face; centered form plus 5 per cent alpha molybdenumt By reducing t-her plating temperature to 330 C. the carbon was 25.5 atomic. per cent and the molybdenum per cent in gamma form. The structure was determined by X-ray examination, the carbon content by analysis.

As an alternative. for some purposes prefferred method, the ingress of carbon monoxide either with or without hydrogen alongwith the metal carbonyl maybe continued during the` enu tire plating process: and these gases may be caused to enter through the. inlet, tube containing the carbon-ylpowder o1? through another tube. The amount of` carbon; monoxide used may var-y in accordance with thcpr-inciples elsewhere herein stated. Also when hydrogen on other gases is or are introduced, this may be through the saine orv a different inlet and for this purpose the; apparatus mayv be provided with as many inlets like Hh asY desired.

The apparatus of Eig; l; thus may be employed to produce coatings of tungsten. carbide (W2C), molybdenum or chromium carbides on metallic objects, such as the object 2.o.- or similar objects such as contacts, filaments or other electrodes, edges or cutting tools or other objects. For example, a nichel 20u for a vacuum tube could be mounted in a ceramic block 21a and coated; with Moe@ or W2C by this method, or a lila-ment Could be coated with W2C.

Fie. 11A represents. a: modifiioation of Fis. l

.as applied tov coat or plate the interior surface of a tubular object Withlittle orno; plating of the. outer suriace. The tubular object 2i! to be plated is traversed by a passage 22o. lt is mounted in a; fram-e of mica which comprises two baffles; 4:2 which substantially ll the cross section of; tube t0; and cause all the carbonyl gas to pass through the passage alle. The outer surface is covered with a mica layer 43; the ends of object 2;!1- are in this; @ase left exposed and are plated. Very little d =r osi-t occursY upon the sui-- iace or the; mica. and that onlyiinon the part which lies close to the object 2e and thus be comes heated,

In Fig. 1B which is amodiiication in part of'lig. l between thelines X-X and Y--Y, two other objects are illustrated in the plating chamber lil. Ordinarily; however, at most onlyv one class of object would be placed in the plating chamber aty a time. These would not necessarily be placed in the positions shown. The principal object of Fig. l'Bis toillustrate methods of plating portions of the surf-'ace of an object to the exclusion of other portions. A clock pinion mounted on` axle lili may be arranged to be plated on a conical end of the axle. A plasticor vitreous body El is made in two or more halves into which the axle lif and its associated wheel,A for example, the wbalanceWheel or pinion, is to be fitted. The

body K55 is mounted on standards or conical supports 2 I. When the hydrogen is applied the axle M becomes heated but the vitreous body 45 does not become heated therefrom for a long time especially as the constant flow of gas including hydrogen carries away the heat fairly rapidly. The plating thus occurs solely upon the conical ends of the axle 45 for the purpose of forming hard bearing surfaces. Platings of tungsten high in interstitial carbide or tungsten carbide may be used for this purpose and platings have been deposited which, on test, were found to be harder than sapphire.

The body 45 may comprise a cylindrical element having a screw threaded portion such as might be utilized for an electrical relay or switch contact to be plated only on its end 41. A plastic or vitreous body 48 may be constructed in two halves and the object 41 placed between the two halves so as to expose only the end i1 which 1s the only portion to be plated. In the particular arrangement a series of openings 49 are provided to permit the flow of gases through the plating chamber to the outlet IE. In other arrangements the body S might not fill the entirety of the cylindrical space in the plating chamber and the openings 49 would be unnecessary.

Fig. 2 illustrates another arrangement of plating the contact surface 55 of a relay armature l. This armature may be placed between the two halves of a vitreous body 52 so that only the contact surfaces 50 are exposed. rlhe assembly 5I, 52 is then placed in the plating chamber in a manner to expose the contact surfaces 50 symmetrically to the stream of carbonyl gas.

Fig. 3 illustrates another arrangement in which a plastic or vitreous body 53 which may consist of glass or porcelain has a number of contact buttons placed upon it so that the upper surfaces and the cylindrical surfaces of the buttons 5s may be plated. The bottom surface resting on the body 53 is substantially unplated and could be welded, or soldered to an armature or other metallic support to serve as an electrical contact.

Fig. 4 illustrates another arrangement in which metallic carbonyls along the carbon monoxide and hydrogen are introduced through pipes I5 and I1b controlled by valves I'Ia and I'Ic to the interior of a plating chamber 55. Plating chamber 55 has an outlet tube I6 leading to a suciently powerful vacuum pump and controlled, if desired, by a valve I8. A water jacket having an inlet tube I2 and an outlet tube I3 surrounds the chamber 55 whose walls 5E are kept cool. A sheet of material 51 to be plated is placed against the end of the chamber 55 and sealed thereto by rubber or copper gaskets 58 and screws 59 which pass through the flanges of a ring SB and hold the sheet 51 in a firm, gas-tight manner against the arm of the plating chamber. A chamber SGA conventionally illustrates a fiue which may be supplied with hot gases from a furnace to heat the sheet 51 to a desired considerably high temperature during the plating operation. Any suitable source of hot gases or appropriate heating means may be employed. The inlet tubes I5 and I1b are connected to a plating head El which is provided on the side towards the sheet 51 with a considerable number of uniform openings 62 through which the plating gases pass to impinge upon the surface of the plate 51. Sheet 51 may consist of glass, vitreous material, any plastic which will withstand the necessary high temperature, and possesses a sufficiently low vapor pressure thereat, or metal sheet of any of the kinds previously enumerated. Sheet 51 need not necessarily be plane but may be curved, be concave or convex or otherwise curved or shaped and the adjacent surface of the plating head '52 may be appropriately shaped in conformity therewith.

Figs. 5 to 9, inclusive, illustrate certain details of an arrangement for plating or coating the interior surface of hollow bodies such as the body 53 which may be long or short and whose interior surface may be straight or curved, grooved or slotted. The body 63 is placed in a cylindrical plating chamber 54 mounted upon a suitable support 65 which is placed in the plating chamber to hold the body 63 in appropriate position. The bottom of the plating chamber is closed by means of a bottom plate 56 held in position by screws 51 and sealed with a copper or other suitable gasket G8. The top of the plating chamber is sealed with a plate S9 held in place by screws 1li also sealed with an appropriate gasket 1I. Through an opening in thertop plate 69 there extends a hollow moving injector 12 for supplying plating gas to the interior bore of the object 63. The moving injector passes through a gastight seal 13 which is more or less conventionally illustrated and may consist of several seals in series. The top and bottom plates 55 and 59 are provided with copper tubes 14 for supplying cooling water during the plating operation. These tubes 15 may be soldered, brazed, or otherwise attached to the end plates SB and as well as to the upper and lower flanges of the main body Sii for the plating chamber so as to conduct heat away therefrom in an efficient manner.

A flexible hose 15 is firmly attached in an air-tight manner to the upper end of the moving injector 12 for supplying carbonyl vapor alongY with hydrogen, carbon monoxide and water vapor, if desired, from suitable sources connected by appropriate piping systems and individually controlled by valves. The moving injector 12 has a bore 15 through which the plating gases pass to the interior of the plating vessel Sil. The moving injector is also kept cool by means of cooling iiuid supplied from inlet tube 'I1 which passes down a tube or passageway 18 on one side of the center tube 66 and back up through another tube 19 to the outlet 80. The inlet and outlet tubes 11 and 85 may be connected by suitable hose connections to an appropriate supply source and disposal source of cooling water or to a radiator. The bottom end of the moving injector 12 is shown in horizontal cross-section in Fig. 7 and in vertical cross-section in Fig. 8. A septum 8l extending across the tubes separates the passageways 18 and 13 and this septum is discontinuous at the bottom so that the passageways 1S and 19 are connected together by an annular opening 82.

When the plating operation is started the moving injector 12 is traversed upwardly and downwardly by means of a reversing screw 83 which has its groove engaged by a pin 3A (Fig. 9) fixedly engaged in a nut 85. When the reversing screw is driven by suitable gears, such as the beveled gears 86, the moving injector is caused to be moved reciprocally upward and downward so that the end moves from the approximate top to the approximate bottom of the element 63 to supply plating gas to cause a uniform plating along the bore of the element 63.

The element 63 may conveniently be heated by conduction through and radiation from the walls of chamber 64 during plating operation by a heating winding 81 which may be insulated with asbestos or other heat-resistant material and packed in asbestos packing 88 which may largely or wholly ll the casing 89 which serves further to reduce the radiation and loss of heat to the surrounding atmosphere. The heating element 8S is conveniently supplied with heating current from any desired alternating current or direct current source.

Outlet tubes I2 are connected to a main outlet tube Iza. which in turn is connected to a suitable vacuum pump or vacuum pump system through valves as may be desired.

The operation of the arrangement of Figs. 5 to 9, inclusive, will now be briey outlined. An object 53 to be plated is placed in the plating chamber upon the Vsupport 65 by removing the bottom plate 66 and then sealing it back to form a gas-tight connection. The heating winding 8l is then energized and as soon as the object 63 is appropriately hot, pure hydrogen gas may be introduced through the tube and the traversing screw started into operation in order to clean the interior of the object 63 by removing foreign substancesI and reducing metallic oxides on the surface. After the cleaning has continued for sufficient time, carbonyl vapor, with or without other gases, may be introduced through the tube 'I5 and the plating operation is commenced. Initially the object 63 is maintained at an appropriate temperature to form an effective bond of the plating on the surface to be plated and thereafter the temperature of the object 83 may be regulated by increasing or decreasing it to a temperature appropriate to the desired speed of plating and the amount of carbonyl vapor, hydrogen, carbon monoxide, with or without other gases, such as water vapor, which may be introduced. At the end of the operation the carbonyl gas is cut oif, the object 63 is allowed to cool and it may then be removed from the plating chamber whereupon the apparatus is in condition for repeating the operation to plate another object.

The arrangements described are exemplary for indicating various types of arrangements which may be employed for plating the whole or parts of surfaces and the parts being of various sizes and shapes.

Tungsten carbide having the formula W2C, with a small variable excess or one or theother of carbon or tungsten, may be plated; this plating is very hard. This hardness is considered to arise in part from the smallness of the crystals in the plate. Note is also made of the fact that the plating is free from iron, nickel, cobalt, or similar elements. Likewise, adherent plating of MolC and MozC or mixtures thereof which are hard can be produced.

Tests of carbides of composition MozC and M040 and upon platings consisting of various proportions of those carbides with molybdenum show that many of these platings have unexpected hardness. They are often composed of fine crystals and under some conditions which may be experimentally determined by X-ray analysis, the crystals have a strong orientation. As previously set forth, pure metals and alloys may also be deposited. In practice the last vestige of carbon cannot be eliminated from the plated metal although under appropriate conditions the carbon content may be made quite small or so small as to be insignificant in affecting the properties of the product.

The hardness combined with toughness in varying degrees together with resistance to corrosion makes the process available for the production of various useful products, such as plated or coated working surfaces for wire drawing dies, cutting tools, machine drills, rolls, engine bearings, valves of internal combustion engines, taps, reamers, metal slitting saws, pinion bearings, nozzles, and rotors and stators of high temperature turbines, as well as the blades of combustion chambers of internal combustion turbines which may be rendered less subject to corrosion by plating with suitable carbides of chromium, tungsten or molybdenum or by a mixture thereof with metals.

Rolls of cylindrical or rolling pin form may be supported at the centers of their ends by ceramic supporting frames including a ceramic holding screw in a manner similar to the method of holding a work piece in a lathe. Similar or analogous methods may be employed to plate the whole or working surface of valves such as the valves of internal combustion engines. The whole or the working faces of precision tools, such as -guages and guage blocks which are required to be hard and of exact dimensions, may also be plated by one or more carbides or by mixed carbides.

A metal coated with an adherent layer as defined herein signifies a condition of powerful adherence whereby the metallic body may be stretched or distorted or subjected to high temperatures or high pressures or both without separating the layer. In the case of tough layers of plated material, this stretching or distortion without cracking or breaking may be consider-l able; when the plated layer is hard and brittle the stretching or distortion may be slight before cracking or breaking, not because the adherence is less but because the plated metal will crack or break upon stretching or distortion but will nevertheless tend to adhere strongly even though cracked. A mere superficial attachment is not considered to be adherence in the sense of this specification.

What is claimed is:

1. The method of plating a surface which comprises maintaining the surface to be plated at a temperature of from 200 C. to 600 C., passing carbonyl vapor of a metal selected from the group consisting of tungsten, chromium and molybdenum together with carbon monoxide in addition to that produced by decomposition of carbonyl and up to 1,000 molecules of hydrogen per molecule of metallic carbonyl over the surface to be plated, and maintaining the pressure at from 0.001 to 12 millimeters of mercury at the surface.

2. The method of claim l in which the surface to be plated is maintained at a temperature of from 500 C. to 600 C. and in which the carbonyl is molybdenum carbonyl.

3. The method of claim 1 in which the surface to be plated is maintained at a temperature of from 450 C. to 500 C. and in which the carbonyl is tungsten carbonyl.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,063,596 Feiler Dec. 8, 1936 2,344,138 Drummond Mar. 14, 1944 2,475,601 Fink July 12, 1949 2,503,509 Germer May 23, 1950 2,516,058 Lander July 18, 1950 2,602,033 Lander July 1, 1952 

1. THE METHOD OF PLATING A SURFACE WHICH COMPRISES MAINTAINING THE SURFACE TO BE PLATED AT A TEMPERATURE OF FROM 200* C. TO 600* C., PASSING CARBONYL VAPOR OF A METAL SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN, CHROMIUM AND MOLYBDENUM TOGETHER WITH CARBON MONOXIDE IN ADDITION TO THAT PRODUCED BY DECOMPOSITION OF CARBONYL AND UP TO 1,000 MOLECULES OF HYDROGEN PER MOLECULE OF METALLIC CARBONYL OVER THE SURFACE TO BE PLATED, AND MAINTAINING THE PRESSURE AT FROM 0.001 TO 12 MILLIMETERS OF MERCURY AT THE SURFACE. 